1. Field of the Invention
The present invention relates to a safety arrangement and more particularly relates to a safety arrangement incorporated with an air-bag ignition circuit.
2. Description of the Related Art
It has been proposed previously to provide an air-bag ignition circuit adapted to provide electrical power to a "squib" or igniter which activates a pyrotechnic charge within the air-bag to inflate the air-bag.
It is important that the "squib" or igniter is not inadvertently activated, but equally it is important that the "igniter" or squib is activated in accident situations.
It has been proposed, therefore, to connect the "squib" or igniter in a series connection between a power supply rail and earth with two separate switches. One switch is termed a "safing sensor ". This switch is adapted to close when subjected to a deceleration force in excess of a predetermined level, which is selected to be a relatively low level, but only after a predetermined period of time has elapsed. A second switch, which may be a transistor switch and which may be termed an igniting transistor is provided which is activated by a sensor, the sensor responding to a high level of deceleration. It is thus apparent that the circuit is only completed when both of the switches are closed.
With the circuit arrangement of this type it is possible for a central processing unit to monitor the condition of the switches, but such monitoring may be subject to software error and is not totally reliable.
The present invention seeks to provide an improved arrangement.